The invention relates to safety locking devices in general, and more particularly to improvements in safety locking devices which can be used with advantage in motor vehicles to releasably secure belts or straps to buckles. Locking devices of the type to which the present invention pertains can be used in conjunction with front lap belts, shoulder belts or combinations of front lap and shoulder belts.
Haglund et al. U.S. Pat. No. 4,454,634 discloses a safety locking device wherein a buckle contains a pivotable coupling member which can releasably hold an inserted tongue. The buckle can be anchored in the seat or elsewhere in the motor vehicle, and the tongue is attached to one end of a belt. A release member is provided to disengage the coupling member so that the tongue is free to leave the buckle. The patented locking device is further equipped with an ejector which can automatically expel the tongue from the buckle when the release member has caused the coupling member to free the tongue for movement relative to the buckle. The release member is a depressible part which is movable in parallelism with the plane of the inserted tongue and is biased to a starting or inoperative position by a coil spring or the like.
Locking devices of the above outlined characters are normally used with so-called lock tighteners. If the tightener is deactivated in the event of an accident, the thus released energy causes acceleration of the entire locking device in a direction toward the floor of the motor vehicle, and the locking device is thereupon abruptly decelerated when it reaches an obstruction while assuming a lower end position. Depending on the design of the locking device, its parts can be subjected to acceleration in the range of 500 to 1000 g. The inertia of the release element is sufficiently pronounced to cause automatic movement of the release member to its operative position and to thus cause the coupling member to free the tongue, i.e., to disengage the free end of the belt from the buckle. This can result in injury to, or in death of, the user of the belt.
In accordance with a proposal which is discussed in published European patent application No. 0 212 507, activation of the aforementioned tightener automatically entails blocking of the release member in its inoperative position. The published application proposes to provide a mass or weight which compensates for the mass of the release member and is connected with the latter by means of a lever. This published application further proposes to modify the just described structure by employing a lever the inertia of which is high and which enters the space between its bearing means and the release member in the event of abrupt acceleration of the locking device. Still further, the published application proposes to combine, or to provide the release member, with a shock absorber which is to prevent abrupt changes of position of the release member in the event of undue acceleration of the locking device.